<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #parent {
            width: 500px;
            height: 500px;
            margin-top: 200px;
            background-color: deeppink;
        }
        #son {
            width: 200px;
            height: 200px;
            background-color: orange;
            margin-top: 200px;
        }
    </style>
</head>
<body>
    <!-- margin塌陷  父子元素 -->
    <div id="parent">
        <div id="son"></div>
    </div>
</body>
</html>